Saturday, September 28, 2013

Warming of the climate
system is unequivocal, and since the 1950s, many of the observed changes are
unprecedented over decades to millennia. The atmosphere and ocean have warmed,
the amounts of snow and ice have diminished, sea level has risen, and the
concentrations of greenhouse gases have increased. Each of the last three
decades has been successively warmer at the Earth’s surface than any preceding
decade since 1850. In the Northern Hemisphere, 1983–2012 was likely the warmest
30-year period of the last 1400 years.

Ocean
warming dominates the increase in energy stored in the climate system,
accounting for more than 90% of the energy accumulated between 1971 and 2010 (high
confidence).
It is virtually
certain that
the upper ocean (0−700 m) warmed from 1971
to 2010, and it likely warmed between the 1870s and 1971. Over the last
two decades, the Greenland and Antarctic ice sheets have been losing mass,
glaciers have continued to shrink almost worldwide, and Arctic sea ice and
Northern Hemisphere spring snow cover have continued to decrease in extent (high confidence).

The
rate of sea level rise since the mid-19th century has been larger than the mean
rate during the previous two millennia (high confidence). Over the
period 1901–2010, global mean sea level rose by 0.19 [0.17 to 0.21] m. The
atmospheric concentrations of carbon dioxide (CO2), methane, and nitrous
oxide have increased to levels unprecedented in at least the last 800,000
years. CO2
concentrations
have increased by 40% since pre-industrial times, primarily from fossil fuel emissions
and secondarily from net land use change emissions. The ocean has absorbed
about 30% of the emitted anthropogenic carbon dioxide, causing ocean
acidification.

Total
radiative forcing is positive, and has led to an uptake of energy by the
climate system. The largest contribution to total radiative forcing is caused
by the increase in the atmospheric concentration of CO2 since 1750. Human
influence on the climate system is clear. This is evident from the increasing
greenhouse gas concentrations in the atmosphere, positive radiative forcing,
observed warming, and understanding of the climate system.

Climate
models have improved since the AR4. Models reproduce observed continental-scale
surface temperature patterns and trends over many decades, including the more
rapid warming since the mid-20th century and the cooling immediately following large
volcanic eruptions (very high confidence).

Observational
and model studies of temperature change, climate feedbacks and changes in the
Earth’s energy budget together provide confidence in the magnitude of global
warming in response to past and future forcing.

Human
influence has been detected in warming of the atmosphere and the ocean, in
changes in the global water cycle, in reductions in snow and ice, in global
mean sea level rise, and in changes in some climate extremes. This evidence for
human influence has grown since AR4. It is extremely likely that human
influence has been the dominant cause of the observed warming since the
mid-20th century.

Continued
emissions of greenhouse gases will cause further warming and changes in all
components of the climate system. Limiting climate change will require
substantial and sustained reductions of greenhouse gas emissions.

Global
surface temperature change for the end of the 21st century is likely to exceed
1.5°C relative to 1850 to 1900 for all RCP scenarios except RCP2.6. It is likely to exceed 2°C
for RCP6.0 and RCP8.5, and more likely than not to exceed 2°C for
RCP4.5. Warming will continue beyond 2100 under all RCP scenarios except
RCP2.6. Warming will continue to exhibit interannual-to decadal variability and
will not be regionally uniform.

Changes
in the global water cycle in response to the warming over the 21st century will
not be uniform. The contrast in precipitation between wet and dry regions and
between wet and dry seasons will increase, although there may be regional exceptions.

The
global ocean will continue to warm during the 21st century. Heat will penetrate
from the surface to the deep ocean and affect ocean circulation.

It
is very
likely that
the Arctic sea ice cover will continue to shrink and thin and that Northern
Hemisphere spring snow cover will decrease during the 21st century as global
mean surface temperature rises. Global glacier volume will further decrease.

Global
mean sea level will continue to rise during the 21st century. Under all RCP
scenarios the rate of sea level rise will very likely exceed that
observed during 1971–2010 due to increased ocean warming and increased loss of
mass from glaciers and ice sheets.

Climate
change will affect carbon cycle processes in a way that will exacerbate the
increase of CO2
in
the atmosphere (high confidence). Further uptake of carbon by the ocean
will increase ocean acidification.

Cumulative
emissions of CO2
largely
determine global mean surface warming by the late 21st century and beyond. Most
aspects of climate change will persist for many centuries even if emissions of
CO2
are
stopped. This represents a substantial multi-century climate change commitment
created by past, present and future emissions of CO2.

'Another contentious topic was how the report should deal with the recent warming hiatus. The draft acknowledged the scientists' concerns and noted that climate models "do not generally reproduce the observed reduction in surface warming trend over the last 10-15 years." This was reportedly met with opposition from some delegates who wanted to remove all references to a slowdown. Some argued that the hiatus had not lasted long enough to be considered a temperature trend. Perhaps they also felt it would be seized on by climate-change deniers.

"We looked at this very carefully," said Stocker. There was, he noted, "not a lot of published literature" on the phenomenon. This was a problem, since the IPCC does not do its own research and can only review published literature. But again, the authors of that passage stuck to their guns, and retained most of the message, though the direct statement about the failings of the models does not appear in the report.'

'The report’s heavy dependence on existing climate models creates further problems. Models, like all scientific theory, have to be tested against real-world observations.

Physicists still continually try to test Einstein’s theory of relativity as new opportunities arise, even though it was first published in 1916. The theory has cleared test after test, but researchers keep trying to find its limits and thereby also the limits of its applications. The most recent test of relativity took place in 2013.

Scientists call such tests “validation.” Experts in model validation say that the climate models frequently cited in the IPCC report are little if any validated. This means that as theory they are fundamentally scientifically unproven.'

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